According to the Daily Star today, the 23-year-old, who was due to play a policeman called Nathan, changed his mind about the part after the soap was axed by Five.
A replacament is now being sought with urgency, as the first scenes involving Nathan are due to be shot this week.
"There was no way Nathan could just be axed as that would have meant re-writing months of work," an insider told the newspaper. "So, as you can imagine, Jack's decision has caused quite a few problems. He was able to get out of the contract because it was a long-term one and that can't be met any more."
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